Tubes with substantially tetragonal (e.g., rectangular or square) cross-sections and reinforced ends are used in many applications, e.g., trailer hitch-receiving tubes mounted at a back end of a vehicle. As is well known in the art, a trailer hitch assembly typically includes a frame portion which is attached to the vehicle's chassis, and the hitch-receiving tube is attached to the frame portion.
In the prior art, the reinforced end may be formed by welding a ring to a tube with a tetragonal cross-section. The ring is rectangular or square, as required to fit onto the tube, and is sized accordingly. However, a reinforced end formed in this way (i.e., one including a ring welded to the tube) is particularly susceptible to corrosion, due to salt and water off the roadway. Also, the welded ring tends to be less aesthetically appealing. A tube 10 with a tetragonal cross-section and a reinforced end 11 formed in this way are shown in FIGS. 1A and 1B.
A particular method of cold-forming the reinforced end is known, and is disclosed in U.S. Pat. No. 6,408,672 (Roe et al.). In this method, an end of a tube which is tetragonal in cross-section is cold-formed into a reinforced end. However, because the tube is tetragonal in cross-section, extreme pressure is required to cause material at the end of the tube to buckle and form as required in accordance with the invention disclosed in Roe et al. A tube 12 with a tetragonal cross-section and a reinforced end 13 formed in this way are shown in FIGS. 2A and 2B. (As will be described, the remainder of the drawings illustrate the present invention.) This prior art method has some obvious disadvantages, e.g., a very large press is required in order to exert the very high pressures needed, and the extreme pressure also causes excessive wear and breakage at the tooling surfaces in contact with the deformed area.